In an inkjet recording method, following diffusion of printers or diversification of needs of a recording form in consumers, in recent years, not only general-purpose plain papers such as PPC papers mainly used for texts but recording media (dedicated papers) having an ink-receiving layer such as glossy papers for photography for the purpose of obtaining high-quality images on a par with silver halide prints have been used. Under these circumstances, aqueous inks to be used for inkjet recording are required to obtain excellent colored images on any recording media.
Furthermore, in pigment inks, scratch fastness of images is very important because a pigment and a medium are separated from each other on dedicated paper.
In order to satisfy such characteristics, there are known a method of adding a block copolymer of ethylene oxide and propylene oxide (see Patent Documents 1 and 2) in an ink; a method of adding an acrylic resin for the purpose of enhancing fixability in addition to a self-dispersion pigment and the subject block copolymer (Patent Documents 3 and 4); a method of dispersing a pigment with a styrene acrylic resin and adding a urethane resin (Patent Document 5); and the like.
However, when the subject block copolymer is merely added as disclosed in Patent Documents 1 and 2, there is involved a problem that in the case of using a pigment, dispersion becomes defective.
Also, the method of adding the subject block copolymer to a self-dispersion pigment and further adding an acrylic resin as disclosed in Patent Documents 3 and 4 involves a problem that though scratch fastness is excellent, color development on plain papers, an aspect of which is an advantage of the self-dispersion pigment, is impaired, and gloss on dedicated papers is insufficient.
The method of dispersing a pigment with a styrene acrylic resin and adding a urethane resin as disclosed in Patent Document 5 involves a problem that though scratch fastness is excellent, color development on plain papers and gloss on dedicated papers are not exceptionally excellent.
Patent Document 1: JP-B-3-43313
Patent Document 2: JP-A-2004-27037
Patent Document 3: Japanese Patent No. 3649389
Patent Document 4: Japanese Patent No. 3915369
Patent Document 5: JP-A-2007-119708